1. Field of the Invention
The present invention relates to a distance measuring apparatus, and more particularly, to a distance measuring apparatus having system flexibility by varying a distance measuring range and a distance measuring resolution according to an environment and circumstance.
2. Description of the Related Art
In general, wireless location awareness technologies employ a method of measuring a present location via wireless communication with another wireless communication device by using a wireless signal. Location information obtained by wireless location awareness technologies is importantly used to effectively utilize information obtained by wireless communication via a more effective network configuration.
To improve accuracy of location awareness in such wireless location awareness technologies, it is very important to accurately detect a distance between two wireless communication devices and there is generally applied a method of calculating the distance by detecting time of arrival (TOA) in wireless communication between the two wireless communication devices to measure a distance. Also, to detect TOA, there is applied a method of detecting TOA by counting predetermined pulses by using a counter and using a value of the counting and frequencies of the pulses.
The present applicant filed “Apparatus and Method for Estimating Distance Using Time of Arrival” (Korean Patent Application No. 2006-0090309, on Sep. 18, 2006). There is disclosed an apparatus for estimating a distance using TOA as shown in FIG. 1.
The apparatus of FIG. 1 includes a reference pulse generator 11 generating a reference pulse having a first frequency f0 at a point in time of transmitting a ranging signal from the first wireless communication device 10 to the second wireless communication device 20; a delay pulse generator 12 generating a delay pulse signal having a second frequency f1 different from the first frequency f0 at a point in time of receiving the a response signal transmitted from the second communication device 20 in response to the ranging signal, the first wireless communication device 10 receiving the response signal; an overlap detector 13 detecting a point in time that the reference pulse and the delay pulse overlap each other; a counter 14 counting one of the reference pulse and the delay pulse until the point in time that the reference pulse and the delay pulse overlap each other; and a distance calculator 15 calculating an amount of time from the point in time of transmitting the ranging signal to the point in time of receiving the response signal by applying the first frequency f0, the second frequency f1, and a count value N of the counter 14 and calculating the distance between the first wireless communication device 10 and the second wireless communication device 20 by using the amount of time.
FIG. 2 is a timing diagram illustrating operations of the apparatus of FIG. 1. Referring to FIG. 2, in the prior application, the amount of time Tx from the point in time t0 of transmitting the ranging signal to the point in time t1 of receiving the response signal is calculated as following Equation 1,
                    Tx        =                              N            ·                                                                          1                                      f                    0                                                  -                                  1                                      f                    1                                                                                              +          δ                                    Equation        ⁢                                  ⁢                  (          1          )                    
The amount of time Tx indicates an amount time of a signal roundtrip between the first wireless communication device 10 and the second wireless communication device 20. Accordingly, when multiplying ½ of the amount of time Tx by the velocity of light, the distance between the two wireless communication devices 10 and 20 may be obtained.
However, since a maximum value capable of being measurable of the amount of time Tx is fixed in the apparatus of the prior application, when the amount of time Tx is greater than a maximum measurable value (TMAX), a distance is hardly measured. That is, the apparatus of the prior application cannot be used when it is required to measure a farther distance due to a change in a distance measuring environment. For example, when the apparatus of the prior application is capable of measuring a distance of 10 m to the maximum, it is impossible to apply the apparatus of the prior application to an environment where it is required to measure a distance of 20 m.
Also, in the apparatus of the prior application, since an accuracy of distance measuring is fixed by frequencies of a reference pulse and a delay pulse, though applied to an environment where a maximum distance to be measured is reduced, it is impossible to increase the accuracy. For example, when the apparatus is capable of measuring a distance of 30 m to the maximum, though the apparatus is applied to an environment where it is required to measure a distance of 10 m, the accuracy is incapable of being improved.